From their FAQ:
pptPlex is a research prototype developed by Microsoft Office Labs as an exploration of an alternative method of presenting Microsoft Office PowerPoint 2007 slides. This plug-in allows you to arrange slides on a canvas then zoom between the slides during the presentation. You can move around the canvas and show groups of slides, individual slides, or even zoom in to show a particular section of a slide.

pptPlex is based on the Plex technology demoed by Bill Gates in the TouchWall at the Microsoft CEO Summit 2008 (also developed by Microsoft Office Labs).

Videos available here:
http://www.officelabs.com/projects/pptPlex/Pages/default.aspx